Technical Field
The present disclosure relates to light-emitting devices and processes for manufacturing such light-emitting devices.
Description of the Related Art
A flip-chip connection technique using an anisotropic conductive film (ACF) is a conventional method for connecting a light-emitting element to a substrate (See JP09-8360A.). The ACF is a resin film in which conductive particles are dispersed. After being arranged between a light-emitting element and a substrate, the film is heated while a pressure is applied to the light-emitting element and the substrate so that the conductive particles are caught between electrodes of the light-emitting element and electrodes of the substrate. In this manner, an electrical connection is established by the conductive particles and at the same time the light-emitting element and the substrate are strongly bonded to each other.
Also, a connection technique using an anisotropic conductive paste (ACP) has been developed (See JP09-008360A and JP11-168235A.). The ACP is a dispersion of conductive particles in an adhesive such as an epoxy thermosetting resin. The ACP is applied to a substrate, and a light-emitting element is thermocompression bonded (usually before the curing of the ACP) to the ACP coat. Thus, the light-emitting element is fixed on the substrate and, similarly to the case of the ACF, the conductive particles are caught between electrodes of the light-emitting element and electrodes of the substrate to establish an electrical connection. By using ACP for flip-chip mounting bonding, the post step in the flip chip mounting in which an underfill material is applied to fill spaces such as gaps between a light-emitting element and a substrate can be eliminated.
The conductive particles in the ACFs or the ACPs tend to absorb part of the light emitted from the light-emitting element. To enhance the light extraction efficiency by reflecting the light emitted from the light-emitting element toward the ACF or the ACP, it is proposed that a light-reflecting layer is disposed on the surface of the light-emitting element on the substrate side (See JP11-168235A) or that light-reflective and insulating particles such as titanium oxide, silicon oxide, barium sulfate, boron nitride, zinc oxide or aluminum oxide are added to the ACFs or the ACPs themselves to impart a light-reflecting function (See JP2012-186322A).
An ESC method is a connection method analogous to the flip chip connection techniques with ACPs or ACFs. This method uses an adhesive containing solder particles as conductive particles, and an electronic element and a substrate are soldered to each other via the solder particles caught at the joints between bumps deposited on electrodes of the electronic element and electrodes disposed on the substrate (See JP2013-45650A).
JP2012-156214A discloses a light-emitting device which includes a light-emitting element that is flip-chip mounted on a substrate having a wiring, the light-emitting device being characterized in that it has an insulating light-reflecting layer disposed on the wiring and has a bump which penetrates through the insulating light-reflecting layer to reach the wiring and thereby connects the light-emitting element to the wiring.